scholarly journals Polar observations of electron density distribution in the Earth’s magnetosphere. 1. Statistical results

2002 ◽  
Vol 20 (11) ◽  
pp. 1711-1724 ◽  
Author(s):  
H. Laakso ◽  
R. Pfaff ◽  
P. Janhunen
Keyword(s):  
Electron Density ◽  
Individual Case ◽  
Auroral Zone ◽  
Average Density ◽  
High Time Resolution ◽  
Polar Cap ◽  
Total Electron Density ◽  
Total Electron ◽  
Magnetospheric Configuration And Dynamics ◽  
Order Of Magnitude

Abstract. Forty-five months of continuous spacecraft potential measurements from the Polar satellite are used to study the average electron density in the magnetosphere and its dependence on geomagnetic activity and season. These measurements offer a straightforward, passive method for monitoring the total electron density in the magnetosphere, with high time resolution and a density range that covers many orders of magnitude. Within its polar orbit with geocentric perigee and apogee of 1.8 and 9.0 RE, respectively, Polar encounters a number of key plasma regions of the magnetosphere, such as the polar cap, cusp, plasmapause, and auroral zone that are clearly identified in the statistical averages presented here. The polar cap density behaves quite systematically with season. At low distance (~2 RE), the density is an order of magnitude higher in summer than in winter; at high distance (>4 RE), the variation is somewhat smaller. Along a magnetic field line the density declines between these two altitudes by a factor of 10–20 in winter and by a factor of 200–1000 in summer. A likely explanation for the large gradient in the summer is a high density of heavy ions that are gravitationally bound in the low-altitude polar cap. The geomagnetic effects are also significant in the polar cap, with the average density being an order of magnitude larger for high Kp; for an individual case, the polar cap density may increase even more dramatically. The plasma density in the cusp is controlled primarily by the solar wind variables, but nevertheless, they can be characterized to some extent in terms of the Kp index. We also investigate the local time variation of the average density at the geosynchronous distance that appears to be in accordance with previous geostationary observations. The average density decreases with increasing Kp at all MLT sectors, except at 14–17 MLT, where the average density remains constant. At all MLT sectors the range of the density varies by more than 3 orders of magnitude, since the geostationary orbit may cut through different plasma regions, such as the plasma sheet, trough, and plasmasphere.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; plasmasphere; polar cap phenomena)

scholarly journals Polar observations of electron density distribution in the Earth’s magnetosphere. 2. Density profiles

2002 ◽  
Vol 20 (11) ◽  
pp. 1725-1735 ◽  
Author(s):  
H. Laakso ◽  
R. Pfaff ◽  
P. Janhunen
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Auroral Zone ◽  
Polar Cap ◽  
Geomagnetic Disturbances ◽  
Activity Data ◽  
Density Peaks ◽  
Spacecraft Potential ◽  
Order Of Magnitude ◽  
Auroral Phenomena

Abstract. Using spacecraft potential measurements of the Polar electric field experiment, we investigate electron density variations of key plasma regions within the magnetosphere, including the polar cap, cusp, trough, plasmapause, and auroral zone. The statistical results were presented in the first part of this study, and the present paper reports detailed structures revealed by individual satellite passes. The high-altitude (> 3 RE) polar cap is generally one of the most tenuous regions in the magnetosphere, but surprisingly, the polar cap boundary does not appear as a steep density decline. At low altitudes (1 RE) in summer, the polar densities are very high, several 100 cm-3 , and interestingly, the density peaks at the central polar cap. On the noonside of the polar cap, the cusp appears as a dense, 1–3° wide region. A typical cusp density above 4 RE distance is between several 10 cm-3 and a few 100 cm-3 . On some occasions the cusp is crossed multiple times in a single pass, simultaneously with the occurrence of IMF excursions, as the cusp can instantly shift its position under varying solar wind conditions, similar to the magnetopause. On the nightside, the auroral zone is not always detected as a simple density cavity. Cavities are observed but their locations, strengths, and sizes vary. Also, the electric field perturbations do not necessarily overlap with the cavities: there are cavities with no field disturbances, as well as electric field disturbances observed with no clear cavitation. In the inner magnetosphere, the density distributions clearly show that the plasmapause and trough densities are well correlated with geomagnetic activity. Data from individual orbits near noon and midnight demonstrate that at the beginning of geomagnetic disturbances, the retreat speed of the plasmapause can be one L-shell per hour, while during quiet intervals the plasmapause can expand anti-earthward at the same speed. For the trough region, it is found that the density tends to be an order of magnitude higher on the day-side (~1 cm-3) than on the nightside (~0.1–1 cm-3), particularly during low Kp.Key words. Magnetospheric physics (auroral phenomena; plasmasphere; polar cap phenomena)

Revisiting the charge density analysis of 2,5-dichloro-1,4-benzoquinone at 20 K

2017 ◽  
Vol 73 (4) ◽  
pp. 654-659 ◽  
Author(s):  
Zhijie Chua ◽  
Bartosz Zarychta ◽  
Christopher G. Gianopoulos ◽  
Vladimir V. Zhurov ◽  
A. Alan Pinkerton
Keyword(s):  
Charge Density ◽  
Electron Density ◽  
Topological Analysis ◽  
Diffraction Measurement ◽  
X Ray Diffraction ◽  
Total Electron Density ◽  
Total Electron ◽  
Structure Factors ◽  
Density Analysis ◽  
Experimental Charge Density

A high-resolution X-ray diffraction measurement of 2,5-dichloro-1,4-benzoquinone (DCBQ) at 20 K was carried out. The experimental charge density was modeled using the Hansen–Coppens multipolar expansion and the topology of the electron density was analyzed in terms of the quantum theory of atoms in molecules (QTAIM). Two different multipole models, predominantly differentiated by the treatment of the chlorine atom, were obtained. The experimental results have been compared to theoretical results in the form of a multipolar refinement against theoretical structure factors and through direct topological analysis of the electron density obtained from the optimized periodic wavefunction. The similarity of the properties of the total electron density in all cases demonstrates the robustness of the Hansen–Coppens formalism. All intra- and intermolecular interactions have been characterized.

scholarly journals Analysis of plasmaspheric plumes: CLUSTER and IMAGE observations

2006 ◽  
Vol 24 (6) ◽  
pp. 1737-1758 ◽  
Author(s):  
F. Darrouzet ◽  
J. De Keyser ◽  
P. M. E. Décréau ◽  
D. L. Gallagher ◽  
V. Pierrard ◽  
...  
Keyword(s):  
High Time Resolution ◽  
Total Electron Density ◽  
Density Profiles ◽  
Total Electron ◽  
In Situ Data ◽  
Spacecraft Potential ◽  
Point Analysis ◽  
Boundary Velocity ◽  
Electron Density Profiles

Abstract. Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles have been derived from the electron plasma frequency identified by the WHISPER sounder supplemented, in-between soundings, by relative variations of the spacecraft potential measured by the electric field instrument EFW; ion velocity is also measured onboard these satellites. The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 min; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations of three plume events and compare CLUSTER in-situ data with global images of the plasmasphere obtained by IMAGE. In particular, we study the geometry and the orientation of plasmaspheric plumes by using four-point analysis methods. We compare several aspects of plume motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary as observed by the wave experiment WHISPER on the four spacecraft, (ii) drift velocity measured by the electron drift instrument EDI onboard CLUSTER and (iii) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

Electron densities and the VSEPR model of molecular geometry

1992 ◽  
Vol 70 (3) ◽  
pp. 742-750 ◽  
Author(s):  
R. J. Gillespie
Keyword(s):  
Electron Density ◽  
Present Status ◽  
Electron Pair ◽  
Molecular Geometry ◽  
Physical Basis ◽  
Valence Shell ◽  
Electron Densities ◽  
Total Electron Density ◽  
Total Electron

This paper reviews the present status of the VSEPR model of molecular geometry in relation to electron densities. The discussion is based on the electron pair domain version of this model. The fundamental postulates of the model are summarized and illustrated by a discussion of the structures of some molecules with five and seven electron pair domains in the valence shell, including the recently discovered ions XeF5− and XeOF6−. The total electron density does not provide any obvious support for the model and although electron density deformation maps do provide some support they are not always reliable. The Laplacian of the electron density, however, shows the presence of valence shell charge concentrations that correspond closely in number and properties to the electron pair domains of the VSEPR model. This correspondence between electron pair domains and valence shell charge concentrations provides a physical basis for a better understanding of the VSEPR model. Keywords: VSEPR model, electron densities, molecular geometry, Laplacian of the electron density, electron pair domain.

Total electron density from thes-electron density

1998 ◽  
Vol 57 (5) ◽  
pp. 3458-3461 ◽  
Author(s):  
Á. Nagy ◽  
E. Bene
Keyword(s):  
Electron Density ◽  
Total Electron Density ◽  
Total Electron

scholarly journals Early results from the Whisper instrument on Cluster: an overview

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1241-1258 ◽  
Author(s):  
P. M. E. Décréau ◽  
P. Fergeau ◽  
V. Krasnoselskikh ◽  
E. Le Guirriec ◽  
M. Lévêque ◽  
...  
Keyword(s):  
Electron Density ◽  
Small Scale ◽  
Data Sets ◽  
Total Density ◽  
Total Electron Density ◽  
Data Set ◽  
Total Electron ◽  
Density Data ◽  
Early Results ◽  
Natural Emissions

Abstract. The Whisper instrument yields two data sets: (i) the electron density determined via the relaxation sounder, and (ii) the spectrum of natural plasma emissions in the frequency band 2–80 kHz. Both data sets allow for the three-dimensional exploration of the magnetosphere by the Cluster mission. The total electron density can be derived unambiguously by the sounder in most magnetospheric regions, provided it is in the range of 0.25 to 80 cm-3 . The natural emissions already observed by earlier spacecraft are fairly well measured by the Whisper instrument, thanks to the digital technology which largely overcomes the limited telemetry allocation. The natural emissions are usually related to the plasma frequency, as identified by the sounder, and the combination of an active sounding operation and a passive survey operation provides a time resolution for the total density determination of 2.2 s in normal telemetry mode and 0.3 s in burst mode telemetry, respectively. Recorded on board the four spacecraft, the Whisper density data set forms a reference for other techniques measuring the electron population. We give examples of Whisper density data used to derive the vector gradient, and estimate the drift velocity of density structures. Wave observations are also of crucial interest for studying small-scale structures, as demonstrated in an example in the fore-shock region. Early results from the Whisper instrument are very encouraging, and demonstrate that the four-point Cluster measurements indeed bring a unique and completely novel view of the regions explored.Key words. Space plasma physics (instruments and techniques; discontinuities, general or miscellaneous)

Acrylonitrile (AN)–Cu9(100) interfaces: Electron distribution and nature of bonded interactions

2003 ◽  
Vol 81 (6) ◽  
pp. 542-554 ◽  
Author(s):  
Petar M Mitrasinovic
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Density Functional ◽  
Electron Distribution ◽  
Atomic Orbital ◽  
Interfacial Interactions ◽  
Total Electron Density ◽  
Total Electron ◽  
Topological Features ◽  
The One

There is a fundamental interest in the investigation of the interfacial interactions and charge migration processes between organic molecules and metallic surfaces from a theoretical standpoint. Quantum mechanical (QM) concepts of bonding are contrasted, and the vital importance of using combined QM methods to explore the nature of the interfacial interactions is established. At the one-electron level, the charge distribution and nature of bonded interactions at the AN–Cu9(100) (neutral and charged (–1)) interfaces are investigated by both the Becke (B) – Vosko (V) – Wilk (W) – Nusair (N)/DZVP density functional theory (DFT) method and the MP2/6–31+G* strategy within the conceptual framework provided by natural bond orbital (NBO) – natural atomic orbital (NAO) population analysis and Atoms-In-Molecules (AIM) theory. By this approach, the interfacial interactions are given physical definitions free of any assumptions and are visualized by using the topological features of the total electron density. A natural link between the electron density on the one side and the shapes (not energies) of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) on the other side is clarified. The question of whether the spatial extents of the HOMO and LUMO resemble the corresponding spatial maps of the negative (charge locally concentrated) and positive (charge locally depleted) Laplacian of the total electron density in [AN–Cu9(100)]–1 is addressed.Key words: AN–Cu9(100) interfaces, NBO–NAO population, electron distribution, AIM, bonded interactions.

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